Can i bring a webpage (node) up/down using irules?

As Arie suggests, an HTTP monitor looking for a specific resource on the webserver, /upordown.txt for example, would suffice. You build your HTTP monitor to perform a get for /upordown.txt, and mark the node up (200) or down (404) based on the response code.

Just have the web server admin put the file upordown.txt wherever it can be checked. If the admin wants to take down the node, then they just remove the file. When they want to turn it back up, just put the file back. No need to complicate this with iRules.